Synthesis of pyrimidine nucleoside phosphates



United States Patent I O FIhis invention relates to the synthesis of pyrimidine neeleesiae "S mGn Qphdsphates afid 2",5'- and 3",d diphbsphates. In this specification, the term pyrimidine? includes both pyrimidine and derivatives thereof, such as uracil and cytosine.

A neucleoside is herein deiined as an N=glycoside of a heteroeyelic base. In the 'nucleosirles of the present inventhese heterdcy'clic pyrimidine-er derivatives thereof.

Examples are: 1) Uridine:

(2) Cytidine:

Ill onziol on 2 s 'OH a at H 1" in El CHgOJP OH 2315342 Patented Dec. 3, 1957 ICC (5) Pyrimidine nucleoside 3',5-diphosphate:

In the above examples R is a pyrimidine group such as uracil or cytosine or pyrimidine itself.

Nucleosides and nucleoside monophosphates (Example 3 above), in general, possess useful therapeutic and biological properties. In addition they may be used as intermediates in the synthesis of nucleoside polyphosphates which also possess useful therapeutic and biological properties. A suitable synthesis of nucleoside polyphosphates from nucleoside .monophosphates is given in my co-pend- I (1949) and Gulland fihe y p l ridate.

ing application, Serial No. 437,006, filed June 15, 1954, and published in the Journal of the American Chemical Society 76, pages 3517 and 5056 (1954).

Nucleosides and nucleoside monophosphates may also be used as intermediates in the synthesis of nucleoside di and triphosphates which also possess useful therapeutic and biological properties. Nucleoside 5'-phosphates have previously been obtained as products of enzymetatic degradation of ribonucleic acids, and have been reported by (John and Volkin in the Journal of Biological Chemistry, 203, (1953). Recently cytidine diphosphate and uridine diphosphate (shown in Examples 4 and 5 above) have been required in certain enzymatic studies.

The problem of chemical phosphorylation of nucleos'ides is one of considerable importance and complexity. The common phosphorylating agents and well known simple methods have not been usedbecause of the wellknown lability of the N-glycosidic linkage, especially in the purine nucleosides. Therefore, more complex phosphorylating agents and techniques have been used.

For example, Levene & Tipson, who reported their work in the Journal of Biological Chemistry 106, 113 (19 30) and 121, 131 (1937), Michelson and Todd,who reported their work in the Journal of the Chemical Society, '2476 and Holiday, who reported their work in Journal of the Chemical Society, 746 1940), used phosphorus oxychloride as the phosphorylating agent, with fair results. Bredereck, Berger and Ehrenberg, who reported their work in Berichte 73, 269 (1940), used di- The most satisfactory resuits were obtained, however, when dibenzyl phosphorochloridat'e was used as the phosphorylatin-g agent. This reagent was also used by Michelson and Todd and reported in the Journal of the Chemical Society, 2476 "(1949).

It is the main object of the present invention to disclose of heat or by the addition of P 0 previously known methods. techmque of Cohn and Volkin, reported in the Journal of The preferred nucleosides of the present invention are defined by the following formula:

The numbers represent the designation of the various carbon atoms in the D-ribose part of the nucleoside. R is a pyrimidine group such as uracil or cytosine or pyrimidine itself.

The nucleoside '-monophosphates are preferably pre- HaC CHs CHzOH where R is a pyrimidine. The nucleoside 2',5- and-335'- diphosphates are preferably prepared using the free nucleoside although they may'also be prepared from the I 2',3-isopropylidene derivative.

It has been generally convenient to follow the course 1 of the synthesis reaction by paper chromatography. 2',3'-

isopropylidene uridine was dissolved in a mixture of phosphorus pentoxide and phosphoric acid at about 60 C,

Aliquot portionswere drawn ofi periodically, diluted, and Y heated to a temperature of about 100 C. for about 2 hours. The purpose of the heating was to hydrolyse the inorganic polyphosphates and to remove the isopropylitastmaee I The isopropylidene uridine gradually dissolved to form a liquid yellow solution. Aliquots of 0.2 cc. were removed at intervals and diluted with 2 cc. of water. The clear solutions were heated at 100 C. for one half hour and then neutralized with 4.5 N lithium hydroxide solution. The supernatant liquid, after separation of lithium phosphate by centrifugation was examined by paper chromatography in the solvent system 1% ammonium sulfate-isopropyl alcohol (1:2 v./v.). Three spots, located by their absorption of ultraviolet light, had R, values corresponding to uridine, uridine 5'-monophosphate and uridine 2'(3'),5-diphosphate. Their relative. concentrations were determined by elution with 3 cc. of 0.01 N hydrochloric acid, and measurement of the optical density of the resulting solutions at 260 mu. Table I records the results thus obtained.

I -Urldine Uridlne 5'- Uridlne 2(3), Time (hours) (percent) phosphate 5'-dlphosphate (percent) (percent) dene group. After a two hour reaction period themain.

product of the reaction was uridine 5'-monophosphate; longer periods of time resulted in some phosphorolytic cleavage of the isopropylidene group to form the diphosphates.

In a large scale (5 g.) two hour experiment, after the hydrolitic treatment, mostof the resulting orthophosphoric acid was removed as lithium phosphate (by the addition of lithium hydroxide). The uridine 5 -monophosphate (the main product) was freed from the small amounts of the accompanying uridine and uridine diphosphates on a,

Dowex 2 ion exchange column. After a water wash which removed uridine, uridine 5-phosphate was eluted, along with the residual orthophosphoric acid, with 0.015 N hydrochloric acid. The R; values of the uridine 5'-monophosphate prepared by this method on paper chromatograms in several solvent systems were identical with those of a sample of uridine 5-monophosphate prepared by The elegant ion exchange Before discussing these results it should be mentioned that the time is variable depending upon the temperature of the reaction. Thus, the lower the temperature, the longer the reaction time.

Thus it is evident from the above table that the reaction time of two hours gives the optimum yield of the required uridine 5-monophosphate. Less reaction time results in an appreciably less conversion of uridine to uridine 5-monophosphate, while greater than two hours results in the greater phosphorolytic cleavage of the isopropylidene group thus forming more of the diphosphates.

Example lI.-Uridine 5 '-m0n0ph0sphate 5 g. of dry 2',3-isopropylidene uridine was phosphorylated with 25 cc. of warm freshly prepared solution of phosphorus pentoxide in 85% phosphoric acid, as described in Example 1. After a reaction period of two hours, 100 cc. of cold water was added and the clear solution heated at 100 C. for one-half hour, when the solution attained a light pink colour. The solution was then neutralized with 4.5 N lithium hydroxide solution to a pH of 9, and the heavy precipitate of lithium phosphate removed by centrifugation, the precipitate being thoroughly washed with three 40 cc. portions of water. The combined filtrate and washings (about 500 cc.) were concentrated under reduced pressure to about cc., when some more lithium phosphate was precipitated. This was removed, by centrifugation, and the supernatant liquid absorbed on the top of a Dowex 2 ion exchange resin (220 Biological Chemistry 203, 319 (1953), which success- 1 fully differentiated uridine 5-monophosphate from the 1somer1c 2- and 3-monophosphates was usedas a further check that the product of the reaction was indeed the 5-isome r. Finally, rigid chemical evidence was also The following examples are given to illustrate the meth- I 0d of preparation of the nucleosides 5-phosphates and 2'(3')5'-d1phosphates by the present application.

- pentoxide in 85 phosphoric acid (11:1,3 w./w.) and the 7 mixture, which was stirred at intervals, was maintainedy: at a temperature of C. with the exclus ion of moisture.

-: obtained concerning'the identity of the reaction product.

:to. 325 mesh; chloride form, in a column 14 cm. long by 4 cm. diameter) and the column washed with water until the optical density fell below 0.05. After removal of the uridine in this way (about 1 litre of water was required) 0.015 N hydrochloric acid was passed through the column at a flow rate of 15 cc. per minute. Optical density at 260 m of the efliuent began to rise after 800 cc. of the solution had passed through the column. Four litres of orthophosphoric acid, were collected before the optical density fell below 0.8 again. This solution was concentrated at 30 to 35 C. under reduced pressure to a volume of 'about'20 cc., the concentrate sucked under a high vacuum for six hours, and the final residue kept in an evacuated desiccator over potassium hydroxide and phosphorus pentoxide for'two days. It was then washed twice with 50 cc. portions of dry ether, dissolved in 10 cc. of anhydrous ethyl alcohol, and the uridine 5-monophosphate precipitatedby the addition of cc. of anhydrous ether. The last operation was repeated twice, the ethereal layer being clarified through centrifugation.

The residual gum, which was almost completely free eeifsea from bft hiiphos plio'rie "aid, changed into a brittle resin on storage in an evacuated desiccator 'over phosphorus pentgnide. This brittle resin was then taken up in 40 cc. of water, and neutralized to pH 9 with 4.5 N lithium hydroxide. To this solution was :added 10 cc. of 2 M barium acetate solution, and the .mixture set aside for several hours. The precipitate of barium phosphate (0.340 g. dry weight, admixed with some barium uridine '-monoph osphate) was removed by centrifugation, and flie'remaining 'bariu'm ur'idine "S monophosphate in soluiron was precipitated by the addition of an equal volume of ethyl alcohol. The product was collected by centrifugation, and washed twice with 25cc. portions of 50% ethyl alcohol, then with ethyl alcdhol"alone, and finally with ether. The yield of hydrated barium salt was 5.42 g. and was found to contain 3.74 g. of free uridine 5- monophosphate (65% yield). Paper chromatography in a number of solvent systems gave a single strong spot, having R; values identical with those obtained using a sample of uridine 5 -monophosphate prepared by the previously used methods. The method of paper chromatography of uridine 5'-monophosphate in a number of solvent systems is being presented to the Journal of American Chemical Society in an article by Hall and Khorana entitled Nucleoside Polyphosphates 111.

Example lII.-Cytidine 5'-phosphate 2,3'-isopropylidene cytidine was phosphorylated as described for the corresponding uridine compound in Example II, except that the time of reaction was one hour at a temperature of 60 C. After this time, water was added and the clear solution heated on a water bath for /2--1 hour. The solution was evaporated to a syrup under vacuum and the syrup extracted twice with ethyl ether. Orthophosphoric acid was removed in this way and the insoluble mixture of cytidine phosphates dissolved in water, neutralized with sodium hydroxide and applied Em top of a Dowex 2 ion exchange resin column (formate orm).

Cytidine 5-phosphate was eluted with 0.02 N formic acid. Evaporation of the formic acid solution gave crystalline cytidine 5'-phosphate in a yield of about 60%.

Example lV.-Uridine 2'(3), 5'-diph0sphate To one gram (4.1 m. mole) of uridine (dried previously at 1l0/0.1 mm. over phosphorus pentoxide for 12 hours) was added 5 cc. of warm freshly prepared phosphorylating agent (see Example II above) and the sealed reaction flask maintained at 60 in an oven. Uridine dissolved under frequent agitation during the first one half hour to form a clear dark syrup. Direct examination by paper chromatography of a suitable amount of the fluid removed after a period of 2.5 hours and diluted with water showed only a small amount of unreacted uridine. After a total period of 20 hours the syrup was dissolved in 60 cc. of water and a. small quantity of 6 N hydrochloric acid added to reduce the pH of the aqueous solution to 0. After being heated at 100 for 15 min utes, the solution was neutralized with 4.5 N lithium hydroxide solution to pH 9.

The heavy precipitate of lithium phosphate was removed by centrifugation and washed thoroughly with small portions of water. The combined supernatants were allowed to pass slowly through a bed (12.5 sq. cm. x 4.2 cm.) of Dowex 2 ion exchange resin (200-325 mesh; chloride form). After a water wash which removed some uridine (about 4.4% of the amount of uridine used), uridine monophosphates and orthophosphoric acid were eluted with .01 N hydrochloric acid+.015 M sodium chloride solution (total volume, 4 litres representing 4.7% of the amount of uridine used). The diphosphates were then eluted with .01 N hydrochloric acid+.1 M sodium chloride solution and found to represent a conversion of 80.6% of the amount of uridine used to the diphosphates.

This eluate was neutralized with.sodiumlhydroxideland then concentrated under partialpressure to about 18 cc. After filtr'ation of the solution, to remove any suspended matter, through a sinter glass funnel,- which was later washed with 2 cc. of water, thepH was adjusted to 9 with lithium hydroxide solution and the barium salts werepr'ecipitated by the addition'of '7 cc.'o'f 2 .M'barium acetate solution and collected through centrifugat'ion. These were washed three times with 50% ethyl alcohol, then ethyl alcohol and ether and allowed to equilibrate with air at room temperature. Wt., 2.52 .g., 75% yield.

Example V.-Cytidine 2'(3),5'-diphosphate A mixture of *two' hundred mg (0.824 m. Maid) of cytidine (previously dried at 1l0/0.1 over phosphorus pentoxide for 12 hours) and 1 cc. of a freshly prepared solution of phosphorus pentoxide in phosphoric acid (1:1.3, W./W.) was heated when cytidine slowly dissolved to give a clear homogeneous syrup. After a period of 20 hours the syrup was dissolved in 15 cc. of water and the solution treated as described above for uridine diphosphate. After removal of lithium phosphate the solution (about 50 cc.) was slowly passed through a Dowex 2 (200-325 mesh; formate form) ion exchange bed (12.5 sq. cm. x 2.0 cm.). After a water wash (1000 cc.) which removed only negligible amount of ultra-violet absorbing material (showing the absence of cytidine), 1500 cc. of 0.01 N formic acid +.05 N sodium formate solution were passed, a flow rate of 15 cc. per minute being maintained during this and the following elutions.

Cytidine monophosphates thus removed corresponded to 4.7% of the amount of cytidine employed. The diphosphates were next eluted with 4.0 N formic acid +.01 M sodium formate (and found to represent 74% of the amount of cytidine employed). Subsequent elution with 1.0 N formic +1.0 M sodium formate removed a small amount of material (about 3% of the amount of-cytidine employed) corresponding presumably to 2', 3', 5-triphosphate. The eluate containing the diphosphates was concentrated to half its volume in vacuo, then diluted with an equal volume of water and reevaporated. This process was repeated four times before the volume was reduced to 25 cc., this solution being freeze-dried.

The residue was dissolved in 2.5 cc. of water, filtered through a fritted glass funnel, which was subsequently washed with 1 cc. of water. To the combined filtrate and washing, after neutralization with 4.5 N lithium hydroxide solution to pH 9, was added 1.6 cc. of 2 M barium acetate solution. Ten cc. of ethyl alcohol was added and the precipitated barium salts were collected by centrifugation and washed thoroughly with three portions of 60% ethyl alcohol, then with ethyl alcohol and ether. Yield 430 mg.

I claim:

1. A process for the preparation of a pyrimidine nucleoside 5-monophosphate which comprises reacting a 2,3'-isopropylidene pyrimidine nucleoside with a mixture of phosphorus pentoxide and phosphoric acid.

2. A process for the preparation of pyrimidine nucleoside monophosphate which comprises reacting a 2',3,- isopropylidene pyrimidine nucleoside with a warm mixture of phosphorus pentoxide and concentrated phosphoric acid.

3. A process as claimed in claim 1 in which the ratio of phosphorus pentoxide to phosphoric acid is 1.3 to 1 on a Weight basis.

4. A process for the preparation of a pyrimidine nucleoside selected from the group consisting of 2',5'-diphosphates and 3,5'-diphosphates which comprises reacting a pyrimidine nucleoside with a mixture of phosphorus pentoxide and phosphoric acid.

5. A process for the preparation of a pyrimidine nucleoside selected from the group consisting of 2',5'-diphosphates and 3,5'-diphosphates which comprises reacting a pyrimidine nucleoside with a mixture of phosphorus pentoxide and phosphoric acid.

6. A process as claimed in claim 5 in which the ratio of phosphorus pentoxide to phosphoric acid is 1.3 to 1 on a weight basis.

7. A process for the preparation of a pyrimidine nucleoside 5-monophosphate which comprises reacting a 2',3-isopropy1idene pyrimidine nucleoside with a mixture of phosphorus pentoxide and phosphoric acid and hydrolysing the reaction product to remove the isopropylidene group.

dine is cytosine.

References .Cited in the file of thispatent 4. UNITED STATES PATENTS I 2,052,029 Harris Aug. 25, 1936 FOREIGN PATENTS 141,280 Australian Mar. 4, 1948 OTHER REFERENCES 

1. A PROCESS FOR THE PREPARATION OF A PYRIMIDINE NUCLEOSIDE 5'' MONOPHOSPHATE WHICH COMPRISES RACTING A 2'',3''-ISOPROPYLIDENE PRYIMIDINE NUCLEOSIDE WITH A MIXTURE OF PHOSPHORUS PENTOXIDE AND PHOSPHORIC ACID. 